1. Field of the Invention
The present invention relates to a motor driving apparatus and it particularly relates to a technique for controlling the rotation frequency of a motor.
2. Description of the Related Art
In a motor driving apparatus that rotates a DC motor or spindle motor at a desired rotation frequency thereof, the rotation frequency of a motor is monitored and a driving signal is generated based on a deviation thereof from a desired target value.
There are cases where a speed discriminator as described in Patent Document 1, for example, is used in the motor driving apparatus that controls the motor in this manner.
The speed discriminator compares the current rotation frequency of the motor with the rotation frequency that serves as the desired target value, and outputs an acceleration pulse or a deceleration pulse according to the deviation. This acceleration pulse and the deceleration pulse are converted to the DC voltage, so that a control voltage for driving the motor is produced.
[Patent Document 1]
Japanese Patent Application Laid-Open No. Hei06-30589.
As described above, the speed discriminator generates the acceleration and deceleration pulses based on the deviation of the current rotation frequency of the motor from the target value of the rotation frequency thereof, so that a feedback path is formed in the motor driving apparatus. A low-pass filter for smoothing the control voltage obtained by converting the acceleration and deceleration pulses is provided in this feedback path.
In such a motor driving apparatus, when the rotation of the motor is started from a motor stoppage state, an acceleration pulse is generated from the speed discriminator and thus the control voltage for driving the motor rises up rapidly. Nevertheless, since high-frequency components are removed by the low-pass filter, a starting time required until the rotation frequency of the motor reaches a desired target value will become longer due to the effect of a time constant of the low-pass filter. Also, since the bandwidth of a feedback path is narrowed by the low-pass filter, an overshoot that exceeds considerably the desired target value may occur and a ringing may occur.